Boost converter circuit is used to boost an input voltage to a higher output voltage. A boost ratio of ten or more is possible, e.g., in portable display applications. A boost converter may be used, e.g., to power a string of white LED diode for LCD backlight. In such situations boost converter may be used to convert a five volt input to an output voltage of up to 50V. A boost converter generally includes five basic components, namely a power semiconductor switch, a diode, an inductor, a capacitor and a modulation controller.
For high power and high output voltage application, a complementary metal-oxide-semiconductor (CMOS) boost controller integrated circuit (IC), an external high voltage N-type field effect transistor (NFET), which provides the necessary blocking voltage, and an external sense resistor are conventionally used as shown in a boost converter 100 of FIG. 1. As shown in FIG. 1, boost converter circuit 100 includes a die pad 102 onto which is mounted a low voltage integrated circuit (IC) containing a controller 104. An external sense resistor Rs and an external high voltage NFET 106 may be coupled to the controller 104. The controller 104 may be any type of modulation controller, such as a pulse-width modulation (PWM) controller. An inductor L may be directly coupled between the input voltage VIN of the controller 104 and a drain D of the NFET 106 at a switch point denoted LX. An external sense resistor Rs may be coupled between a source S of the NFET 106 and ground. An external high voltage (HV) Schottky diode DSch, and a capacitor C may be coupled in series between the drain D and the ground. An output voltage VOUT may be obtained at a point between the Schottky diode DSch, and the capacitor C. There may be a voltage drop VDIODE across the Schottky diode. This type of boost converter circuit 100 may be applied in high voltage, high power applications with low-side or high-side current sense. Such applications may use an external high voltage NFET and an external high power sense resistor at the high side or low side. The external sense resistor may ease the high voltage requirement for the controller IC 104. However, the total size of the low voltage CMOS IC, the external high power resistor and the external high power FET is often larger than is desirable for board space sensitive applications such as portable template DVD players, ultra-compact portable personal computers. In addition, the external sense resistor and the external high power FET increase the total Bill of Material (BOM) Cost.
For low power but high output voltage applications, a fully integrated boost converter with CMOS or Bipolar Controller and DMOS or Bipolar boost switch is sometimes used, e.g., as shown in FIG. 2. Similar to boost converter circuit 100 as described above, a boost converter 200 may include an inductor L directly coupled to the input voltage VIN and coupled to an output voltage VOUT through an external high voltage (HV) Schottky diode DSch and a capacitor C provides smoothing of the output voltage VOUT. The boost converter 200 may also include a low voltage controller 204, a high voltage NFET and a high voltage current sense resistor 206, all of which are built on a multi-voltage IC 202, which must be high voltage-rated.
For low power but high output voltage applications, a fully integrated Boost Converter may achieve a small form factor. However, the production cost may be too high due to the custom nature of the high voltage IC processes, which require a maximum voltage rating (Vout+Vdiode) dictated by process limitations.
It is within this context that embodiments of the present invention arise.